Limiting oxygen index (LOI) of the most of the textiles in use have lower than 21%, while cotton has 18.4%, which means that they can burn easily once the fire has started. Currently, there is some difficulty in making durable flame retardant (DFR) treatments for cotton fabric using an ordinary one step wet process, which is nontoxic to the humans and the environment. This research has also aimed to investigate the optimum treatment conditions that allow controlled deposition of zinc oxide onto carboxymethylated cotton fabric using sodium hypophosphite (SHP) /citric acid (CA). In this regards, the influence of the process parameters on the physicochemical and performance properties of treated cotton fabric will elucidate. The treated fabric was monitored for carboxylic content, LOI, char length, char residue, whiteness index, retained tensile strength and elongation at break. The formation of zinc oxide was verified using UV-Visible spectrum at wavelength of 325nm. Also, the zinc oxide in nano scale was monitored and observed in the range of 19-41nm by transition electron microscope (TEM). The treated cotton fabrics show LOI value and char length 25.3%, 3cm respectively, compared with 18.4 and 11cm for untreated fabric. The existence of zinc oxide particle interaction and other functional groups introduced into cotton fabrics were promoted by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and X-ray diffraction (XRD).